Depending on the applications envisaged, thermal stabilization during shaping or during the use of the corresponding products is carried out in various ways.
French Patent FR-A-2,297,227 describes PVC compositions stabilized effectively by metal-organic salts such as salts of zinc, calcium and barium and .beta.-diketones.
These compositions also contain common additives such as epoxidized oils, lubricants, plasticizers or impact strength enhancing agents.
For some applications, especially those for which the chlorinated polymer has to be plasticized to only a small extent, if at all, the customary presence of relatively large amounts of epoxidized oil, such as epoxidized soybean oil or epoxidized linseed oil, in the polymer, tends to lower the softening point of the polymer.
In fact, the elimination or a significant decrease in the content of these epoxidized oils tends to decrease the thermal stability of the polymer compositions.
This manifests itself, during thermo-forming of the compositions, in a substantial yellowing of the polymer, which is unacceptable for applications requiring transparency and a colorless or only slightly colored appearance of the shaped article, for example, in the case of PVC containers.